Low iron loss and low noise grain-oriented electrical steel sheet and a method for producing the same

ABSTRACT

The object of the present invention is to provide a low iron loss and low noise grain-oriented electrical steel sheet for securing both low core loss and low noise of a transformer at the same time.  
     The present invention relates to a grain-oriented electrical steel sheet containing Si: 1.0-4.0 wt% produced by controlling, with regard to ε O , which is defined as a 0-p value when a grain-oriented electrical steel sheet is magnetized up to a saturated magnetic flux density, and ε 17 , which is defined as the value obtained by subtracting a 0-p value at the magnetization magnetic flux density of 1.7 T from a 0-p value at a saturated magnetic flux density, ε OC  and ε 17L , which are absolute values deviated by forming a tension film and a forsterite film, and ε OL  and ε 17L ,which are absolute values deviated by irradiating laser after the film formation, in adequate ranges respectively, and further controlling λ 17 ,is a 0-p value at the magnetization magnetic flux density of 1.7 T, in the most appropriate range, when measuring a 0-p value of magnetostriction vibration in the rolling direction.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a grain-oriented electricalsteel sheet used for the iron core of a transformer, etc and, morespecifically, to a low iron loss and low noise grain-oriented electricalsteel sheet contributing to lowering not only the iron loss but also thenoise of an iron core, and a method for producing the same.

[0003] 2. Description of the Related Art

[0004] In recent years, it has been desired to reduce the noise andvibration of devices, in which electromagnetism is applied, such astransformers, and it has increasingly been required that agrain-oriented electrical steel sheet used for the iron core of atransformer is a material having not only low iron loss but also lownoise and low vibration. It is said that magnetostriction of agrain-oriented electrical steel sheet is one of the causes for the noiseand vibration of a transformer. Magnetostriction, as cited here, meansthe vibration generated in the rolling direction of the steel sheet whena grain-oriented electrical steel sheet is magnetized by alternatingcurrent, and the magnitude is as small as about 10⁻⁶. However, it hasnot been clarified what kinds of magnetostriction properties areeffective for lowering the noise of a transformer.

[0005] The measure to lower noise has so far been to reducemagnetostriction. It is known that magnetostriction can be lowered byincreasing the integration degree in the orientation of {110}<001> ofsecondary recrystallization grains. This is the same common measure asemployed when iron loss reduction is required. As one of the proposalsfor materials in which magnetostriction is positively lowered, JapaneseUnexamined Patent Publication No. H8-269562 is disclosed. In thispublication, it is attempted to lower magnetostriction by intentionallyleaving internal residual strains at annealing. However, by this method,hysteresis loss increases, causing an increase in iron loss, since thestrains remain.

[0006] As mentioned above, the magnetostriction properties of a materialfor an iron core designed to lower the noise of a transformer have notclearly been proposed so far, and also those of a material to lowermagnetostriction vibration have scarcely been proposed.

SUMMARY OF THE INVENTION

[0007] The object of the present invention is to provide a gran-orientedelectrical steel sheet most suitable for securing both the low iron lossand the low noise of a transformer at the same time, namely, agrain-oriented electrical steel sheet containing Si: 1.0-4.0 wt% withlow iron loss and low noise, and to provide a method for producing thesame.

[0008] The present inventors, as a result of precisely investigating therelationship between the magnetostriction of a grain-oriented electricalsteel sheet and the noise of a transformer and studying various materialfactors affecting the magnetostriction, have found out the fact that, asthe factors of dominating magnetostriction, the tension of an insulationfilm and the imposition of fine strains by laser irradiation are veryimportant in addition to the aforementioned integration degree in theorientation of {110}<001>, and have developed a steel sheet having lowiron loss, and magnetostriction properties for lowering noise, byappropriately controlling those factors.

[0009] The gist of the present invention is as follows:

[0010] (1) A low iron loss and low noise grain-oriented electrical steelsheet, having:

[0011] ε_(OC), an absolute value deviated by forming a tension film froma standard value which is defined as ε_(O) in the state that a tensionfilm substantially does not exist and laser is not irradiated, andε_(OL), an absolute value deviated by irradiating laser after the filmformation from the same standard value, satisfying the followingexpressions;

ε_(OC)<3.0×10⁻⁶

ε_(OC)<1.0×10⁻⁶,

[0012] wherein ε₀ . is defined as a zero-peak value of magnetostrictionvibration when a grain-oriented electrical steel sheet is magnetized upto a saturated magnetic flux density at the frequency of 50 Hz in therolling direction; and

[0013] ε_(17C), an absolute value deviated by forming a tension filmfrom a standard value which is defined as ε₁₇ in the state that atension film substantially does not exist and laser is not irradiated,and ε_(17L), an absolute value deviated by irradiating laser after thefilm formation from the same standard value, satisfying the followingexpressions;

ε_(17C)<1.5×10⁻⁶

ε_(17L)<0.3×10⁻⁶,

[0014] wherein ε₁₇ , is defined as the value obtained by subtracting azero-peak value of magnetostriction vibration at the magnetizationmagnetic flux density of 1.7 T from a zero-peak value ofmagnetostriction vibration at a saturated magnetic flux density at thefrequency of 50 Hz in the rolling direction; and further λ₁₇, azero-peak value of magnetostriction vibration at the magnetizationmagnetic flux density of 1.7 T, satisfying the following expression;

−0.5×10⁻⁶≦λ₁₇≦0.5×10⁻⁶;

[0015] when magnetizing a grain-oriented electrical steel sheet at thefrequency of 50 Hz in the rolling direction and measuring a zero-peakvalue (0-p value: the value of expansion or contraction at a certainmagnetization magnetic flux density determined on the basis of the valuein the state of demagnetization, which is positive in case of expansionand negative in case of contraction) of magnetostriction vibration inthe rolling direction.

[0016] (2) A method for producing a low iron loss and low noisegrain-oriented electrical steel sheet containing Si: 1.0-4.0 wt%comprising the step of determining a heat-input amount of laserirradiation to the unit of area of the steel sheet in accordance with atotal amount of tension obtained by a primary film formed by a finishannealing and a secondary film formed by subsequent processes.

[0017] (3) A low iron loss and low noise grain-oriented electrical steelsheet according to the item (1), having: ε_(OC) and ε_(OL) satisfyingthe following expressions;

ε_(OC)<2.0×10⁻⁶

ε_(OL)<.0.8×10⁻⁶; and

[0018] ε_(17C) and ε_(17L) satisfying the following expressions;

ε_(17C)<1.0×10⁻⁶

ε_(17L)<0.3×10⁻⁶.

[0019] (4) A method for producing a low iron loss and low noisegrain-oriented electrical steel sheet containing Si: 1.0-4.0 wt%comprising the step of; applying a total amount of tension of more than1 MPa and less than 8 MPa which is obtained by a primary film formed bya finish annealing and a secondary film formed by subsequent processes,and

[0020] irradiating laser beam in an amount of heat-input of 1-2 mJ/mm²to the specific unit of area of the steel sheet.

[0021] (5) A low iron loss and low noise grain-oriented electrical steelsheet according to the item (1), having

[0022] ε_(OC) and ε_(OL) satisfying the following expressions;

1.0×10⁻⁶≦ε_(OC)<3.0×10⁻⁶

0.5×10⁻⁶≦ε_(OL)<1.0×10⁻⁶,

[0023] and having ε_(17C) and ε_(17L) satisfying the followingexpressions;

0.5×10⁻⁶≦ε_(17C)<1.5×10⁻⁶

ε_(17L)<0.3×10⁻⁶.

[0024] (6) A method for producing a low iron loss and low noisegrain-oriented electrical steel sheet containing Si: 1.0-4.0 wt%comprising the step of; applying a total amount of tension of more than14 MPa which is obtained by a primary film formed by a finish annealingand a secondary film formed by subsequent processes, and

[0025] irradiating laser beam in an amount of heat-input of 1.5-3 mJ/mm²to the specific unit of area of the steel sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 is a graph showing the 0-p value of magnetostrictionvibration varied by a magnetic flux density on the basis of the value inthe state of demagnetization.

[0027]FIG. 2 is a graph showing the 0-p value of magnetostrictionvibration varied by a magnetic flux density on the basis of the value inthe state of a saturated magnetic flux density.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0028] The present invention will hereunder be explained in detail.

[0029] A grain-oriented electrical steel sheet has three easy directionsof magnetization, namely, [100], [010] and [001]. When a regionmagnetized in a direction different from the direction of a magneticfield is oriented in the direction of the magnetic field with theimposition of the magnetic field or a region oriented in the directionof a magnetic field is oriented in another easy direction ofmagnetization, expansion or contraction is generated, namely,magnetostriction is observed in the direction of the imposed magneticfield.

[0030] In an ideal grain-oriented electrical steel sheet having thegrains completely arranged in the orientation of {110}<001>, themagnetic domain structure is composed of the regions magnetized only inthe rolling direction, namely, of only 180° magnetic domains. Therefore,magnetostriction does not occur during magnetization.

[0031] However, in practice, closure domains called lancet magneticdomains exist in the steel sheet to decrease the magnetostatic energycaused by the deviation of orientation. Further, closure domains existin the regions where strains are introduced and at the edge portions ofthe steel sheet too. The closure domains have regions magnetized in thethickness direction therein, and magnetostriction changes to plus(expansion) when those regions decrease, while it changes to minus(contraction) when they increase.

[0032] The magnetostriction 0-p value of a grain-oriented electricalsteel sheet where a forsterite film or a tension insulation film is notformed and laser beam is not irradiated, as shown by the curve 1-(A) inFIG. 1, increases monotonously with the increase of the magnetizationmagnetic flux density. This is because the aforementioned lancet domainsexist depending on the integration degree of orientation in the state ofdemagnetization and thus their volume is reduced with the application ofmagnetization.

[0033] When a tension insulation film is applied to a steel sheet, asshown by the curve 1-(B) in FIG. 1, the magnetostriction once decreasesbut turns to increase at a high magnetic flux density of about 1.7 T orhigher. The reason is as follows;

[0034] Since the energy at the portions magnetized in the thicknessdirection increases by a magnetoelastic effect when tension is imposedon a steel sheet, the volume of lancet magnetic domains in the state ofdemagnetization decreases compared to the case that tension is notimposed. When a magnetic field is imposed on this, the displacement of180° magnetic domain walls occurs and, since this increases themagnetostatic energy at the surface, lancet magnetic domains increase soas to decrease the magnetostatic energy. Therefore, the steel sheetcontracts in this magnetic field. When the magnetic field is furtherintensified and the displacement of 180° magnetic domain wallsterminates, magnetization proceeds while lancet magnetic domains aredisappearing. In this case, the steel sheet expands.

[0035] In the aforementioned curves of 1-(A) and 1-(B), since the stateof saturated magnetization is the same as the state that magnetizedcomponents in the directions other than the rolling direction disappear,the change of the magnetic domain structure can easily be studied byadopting this state as the basis of expansion and contraction.

[0036]FIG. 2 shows the dependency of a magnetostriction 0-p value on amagnetic flux density setting the magnetostriction 0-p value atsaturated magnetization to zero. In case of a steel sheet where atension film is not applied, as shown by the curve 2-(A), themagnetostriction 0-p value decreases monotonously with the decrease ofthe magnetic flux density. On the other hand, in case of a steel sheetwhere a tension film is applied, as shown by the curve 2-(B), themagnetostriction 0-p value decreases once but increases after reachingthe minimum value. In the state of demagnetization, the steel sheet of2-(B) expands by the value of ε_(OC), as shown in the figure, comparedto the steel sheet of 2-(A).

[0037] Further, with regard to the minimum value, the magnetic fluxdensity where the 0-p value becomes the minimum depends on the degree oforientation of a steel sheet to the orientation of {110}<001>, and ithas been found that the magnetic flux density where the 0-p valuebecomes the minimum is about 1.7 T in case of a conventionalgrain-oriented electrical steel sheet as a result of the investigationby the present inventors. Therefore, in the ε₁₇ defined before, thesteel sheet of 2-(B) expands by the value of ε_(17C) compared to thesteel sheet of 2-(A) at the minimum value of 2-(1). The ε_(OC) andε_(17C) valves can be freely controlled by changing the tension of aninsulation film.

[0038] Further, the present inventors have found out thatmagnetostriction properties can be controlled freely by irradiating witha laser beam after a tension film is formed to the steel sheet. Theeffects will be explained hereunder.

[0039] When laser is irradiated to a steel sheet with a tension filmshown by the curve 1-(B) in FIG. 1, the magnetostriction 0-p valuevaries as increasing monotonously. It is thought that this is becauseclosure domains are formed as the laser irradiation introduces strainsin the steel sheet and then the closure domains disappear with theapplication of magnetization.

[0040] The case where a saturated magnetization state is adopted as thebasis is shown in FIG. 2. The curve 2-(C) which is the case of laserirradiation to a steel sheet with a tension film declines with thedecrease of the magnetic flux density and, in the state ofdemagnetization, the steel sheet contracts by ε_(OL) as shown in thefigure compared with the curve 2-(B). With regard to ε₁₇ defined inrelation to 1.7 T, the steel sheet contracts by ε_(17L). The ε_(OL) andε_(17L) valves can be controlled freely by changing laser irradiationenergy.

[0041] Moreover, the present inventors have earnestly studied how themagnetostriction properties of a grain-oriented electrical steel sheetshould be set to reduce the noise of a transformer and the like and, asa result, have found that the most important feature is to control thepredetermined value of λ₁₇ which is magnetstriction 0-p value on amagnetic flux density defined in relation to 1.7 T for reducing noisecaused by the electric devices in addition to minimizing the amplitudeby vibration. In other word, it is dispensable to control the value ofλ₁₇ satisfying the following expressions;

−0.5×10⁻⁶≦λ₁₇≦0.5×10⁻⁶.

[0042] when λ₁₇ is small, the higher harmonic wave components ofmagnetstriction vibration is increases. On the other hand, when λ₁₇ islarge, magnetstriction vibration expands. These phenomenons arecontribute to increase noise of a transformer. It has been also foundout that, to obtain such a material, it is necessary to control filmtension and laser irradiation energy adequately so that theaforementioned ε_(OC), ε_(OC), ε_(17C) and ε_(17L) are in the rangesbelow,

[0043] ε_(OC)<3.0×10⁻⁶

[0044] ε_(OL)<1.0×10⁻⁶

[0045] ε_(17C)<1.5×10⁻⁶

[0046] ε_(17L)<0.3×10⁻⁶

[0047] and further λ₁₇,which is a 0-p value at the magnetizationmagnetic flux density of 1,7 T, satisfies the expression below,

−0.5×10⁻⁶≦λ₁₇≦0.5×10⁻⁶.

[0048] When film tension is decreased, ε_(OC) and ε_(17C) decrease.However, when film tension is excessively decreased, the deteriorationof magnetostriction is intensified when stress is imposed on a steelsheet during transportation or assembly work of a transformer and thencore loss deteriorates also. Therefore, it is preferable that the valuesof each of ε_(OC) and ε_(17C) is set at more than 0.1×10⁻⁶. Further,since those values have upper limits depending on the integration degreeof orientation, ε_(OC) and ε_(17C) are set at less than 3.0×10⁻⁶ andless than 1.5×10⁻⁶ respectively.

[0049] ε_(OL) and ε_(17L) become large as the laser irradiation energyintensifies. Therefore, ε_(OL) is set at more than 0.1×10⁻⁶ and ε_(17L)at not less than 0. On the other hand, when the laser irradiation energyis excessively large, the amplitude of magnetostriction vibrationbecomes large and the noise when a steel sheet is assembled into atransformer becomes large. Therefore, ε_(OL) is set at less than1.0×10⁻⁶ and ε_(17L) at less than 0.3×10⁻⁶.

[0050] Film tension can be controlled by adjusting the amount of aforsterite film formed after finishing annealing and the amount andcomponent of an insulation film applied thereon. Laser irradiation canbe applied by using a CO₂ laser or a YAG laser. From the viewpoint ofcore loss reduction, it is desirable that the region where strains areintroduced by laser extends in a long and narrow shape to the directionperpendicular to the rolling direction of a steel sheet and the strainband is introduced cyclically in the rolling direction.

[0051] Further, it has been found that the desired magnetic propertiesare varied in accordance with the designed magnetic flux density. Whenthe designed magnetic flux density is relatively small, a relativelyweak film tension is rather effective for further smoothing the waveformof magnetostriction of a steel sheet, reducing the higher harmonic wavecomponent of vibration and thus reducing the noise of a transformer.However, this means causes the deterioration of core loss. Lowmagnetostriction and low core loss have been successfully realized byirradiating a laser beam appropriately and applying magnetic domaincontrol. The steel sheet is an electrical steel sheet having ε_(OC) andε_(OL) controlled in the ranges of

[0052] ε_(OC)<2.0×10⁻⁶ and

[0053] ε_(OL)<0.8×10⁻⁶, respectively, and,

[0054] ε_(17C), ε_(17L) and λ₁₇ in the ranges of

[0055] ε_(17C)<1.0×10⁻⁶,

[0056] ε_(17L)<0.3×10⁻⁶ and −0.5×10⁻⁶≦λ₁₇≦0.5×10⁻⁶, respectively.

[0057] Further yet, the above mentioned electrical steel sheet can beproduced by controlling a forsterite film and an insulation film whosetotal tension having more than 1 MPa and less than 8 MPa, andcontrolling a heat-input laser irradiating energy in an amount of 1-2mJ/mm2 to the specific unit of area of the steel sheet.

[0058] When the tension of an insulation film is small, thedeterioration of magnetostriction increases when stress is imposed on asteel sheet during transportation or assembly work of a transformer andthen iron loss deteriorates also. Therefore, the tension is set at notless than 1 MPa. On the other hand, when the tension is too strong, ahigher harmonic wave component becomes to be included abundantly in thewaveform of magnetostriction vibration and therefore the tension is setat less than 8 MPa.

[0059] On the other hand, when the designed magnetic flux density islarge, it is necessary to strengthen tension to be applied to the steelsheet, and to control the degree of heat-input of the laser irradiationenergy in an appropriate value in accordance with the applied filmtension. As a result, the value of λ₁₇ can be set in the predeterminedvalue. In addition, the magnetstriction vibration can be reduced in asmall value in the ranges of from high magnetic flux density to lowmagnetic flux density. It is desirable to control the values of ε_(OC),ε_(OL), ε_(17C), ε_(17L) and λ₁₇ satisfying the following expressions;

[0060] 1.0×10⁻⁶≦ε_(OC)<3.0×10⁻⁶

[0061] 0.5×10⁻⁶≦ε_(OL)<1.0×10⁻⁶

[0062] 0.5×10⁻⁶≦ε_(17C)≦1.5×10⁻⁶

[0063] ε_(17L)<0.3×10⁻⁶, and

[0064] −0.5×10⁻⁶≦λ₁₇≦0.5×10⁻⁶.

[0065] For realizing the above mentioned features, a production methodis carried out by the steps of applying a total amount of tension ofmore than 14 MPa which is obtained by a primary film formed by a finishannealing and a secondary film formed by subsequent processes, andirradiating laser beam in an amount of heat-input of 1.5-3 mJ/mm² to thespecific unit of area of the steel sheet.

EXAMPLE 1

[0066] In a grain-oriented electrical steel sheet containing Si: 1.0-4.0wt% with the thickness of 0.23 mm processed up to finishing annealing bya conventional method, the thickness of a forsterite film and thecoating amount of an insulation tension film were controlled and thefilm tension was varied. Further, a laser beam was irradiated on thesteel sheet with the irradiation pitch of 5 mm in the rolling directionand the same of 0.03 mm in the transverse direction while varying pulsedenergy. A YAG laser was used in this test. The irradiation energy isexpressed by the energy introduced to a unit area of a steel sheet. Amagnetostriction measuring device of the laser Doppler type was used formeasuring magnetostriction and ten pieces, in each condition, weretested. Table 1 shows the conditions of preparing the test pieces andthe results of the magnetostriction measurement on the average of theten test pieces.

[0067] Further, three phase three legs (Limbs) stacked iron cores in thesize of 750 mm×750 mm were fabricated using the steel sheets of eachcondition and the noise was measured. The width of the steel sheets was150 mm and the number of stacked sheets was 180. In case of zero filmtension, insulation films which do not generate tension were employed.The results are shown in Table 2. By using the steel sheets according tothe present invention, transformers with low noise were obtained. Theiron loss of iron cores is also shown in the table and it is shown thatthe present invention can provide good iron loss. TABLE 1 Film Lasertension energy ε_(0C) ε_(0L) ε_(17C) ε_(17L) λ₁₇ (MPa) (mJ/mm²) (10⁻⁶)(10⁻⁶) (10⁻⁶) (10⁻⁶) (10⁻⁶) A 14 2 1.5 0.4 0.6 0 −0.1 Invention exampleB 8 2 1.5 0.4 0.6 0 +0.2 Invention example C 6 2 1.3 0.5 0.6 0.1 +0.3Invention example D 6 1 1.4 0.2 0.6 0 0 Invention example E 2 1 0.5 0.20.4 0 +0.3 Invention example F 16 2.5 2.0 0.8 0.8 0.2 −0.2 Inventionexample G 15 20 1.5 1.9 0.6 0.5 +0.8 Comparative example H 6 10 1.4 1.20.6 0.3 +1.0 Comparative example I 2 10 0.4 1.3 0.4 0.2 +1.2 Comparativeexample J 0 10 0 1.2 0 0 +1.3 Comparative example K 0 0 0 0 0 0 +0.4Comparative example

[0068] TABLE 2 Transformer noise Iron loss (dB (A)) (W/kg) f = 50 Hz, Bm= 1.7 T f = 50 Hz, Bm = 1.7 T A 42 0.97 B 43 0.98 C 41 0.98 D 43 0.99 E41 1.01 F 40 0.95 C 49 1.03 H 48 1.05 I 50 1.10 J 55 1.30 K 54 1.60

[0069] A grain-oriented electrical steel sheet according to the presentinvention can be produced by adjusting film tension and irradiated laserenergy so that ε_(OC), ε_(OL), ε_(17C), ε_(17L) and λ₁₇ are controlledin prescribed ranges respectively, and can secure both low core loss andlow noise of a transformer at the same time.

1. A low iron loss and low noise grain-oriented electrical steel sheet,having: ε_(OC), an absolute value deviated by forming a tension filmfrom a standard value which is defined as ε_(O) in the state that atension film substantially does not exist and laser is not irradiated,and ε_(OL), an absolute value deviated by irradiating laser after thefilm formation from the same standard value, satisfying the followingexpressions; ε_(OC)<3.0×10⁻⁶ ε_(OL)<1.0×10⁻⁶, wherein ε_(O) is definedas a zero-peak value of magnetostriction vibration when a grain-orientedelectrical steel sheet is magnetized up to a saturated magnetic fluxdensity at the frequency of 50 Hz in the rolling direction; and ε_(17C),an absolute value deviated by forming a tension film from a standardvalue which is defined as ε₁₇ in the state that a tension filmsubstantially does not exist and laser is not irradiated, and ε_(17L),an absolute value deviated by irradiating laser after the film formationfrom the same standard value, satisfying the following expressions;ε_(17C)<1.5×10⁻⁶ ε_(17L)<0.3×10⁻⁶, wherein ε₁₇ is defined as the valueobtained by subtracting a zero-peak value of magnetostriction vibrationat the magnetization magnetic flux density of 1.7 T from a zero-peakvalue of magnetostriction vibration at a saturated magnetic flux densityat the frequency of 50 Hz in the rolling direction; and further λ₁₇, azero-peak value of magnetostriction vibration at the magnetizationmagnetic flux density of 1.7 T, satisfying the following expression;−0.5×10⁻⁶≦λ₁₇≦0.5×10⁻⁶; when magnetizing a grain-oriented electricalsteel sheet at the frequency of 50 Hz in the rolling direction andmeasuring a zero-peak value (0-p value) of magnetostriction vibration inthe rolling direction.
 2. A method for producing a low iron loss and lownoise grain-oriented electrical steel sheet containing Si: 1.0-4.0 wt%comprising the step of determining a heat-input amount of laserirradiation to the unit of area of the steel sheet in accordance with atotal amount of tension obtained by a primary film formed by a finishannealing and a secondary film formed by subsequent processes.
 3. A lowiron loss and low noise grain-oriented electrical steel sheet accordingto claim 1, having: ε_(OC) and ε_(OL) satisfying the followingexpressions; ε_(OC)<2.0×10⁻⁶ ε_(OL)<0.8×10⁻⁶; and ε_(17C) and ε_(17L)satisfying the following expressions; ε_(17C)<1.0×10⁻⁶ ε_(17L)<0.3×10⁻⁶.4. A method for producing a low iron loss and low noise grain-orientedelectrical steel sheet containing Si: 1.0-4.0 wt% comprising the stepof; applying a total amount of tension of more than 1 MPa and less than8 MPa which is obtained by a primary film formed by a finish annealingand a secondary film formed by subsequent processes, and irradiatinglaser beam in an amount of heat-input of 1-2 mJ/mm² to the specific unitof area of the steel sheet.
 5. A low iron loss and low noisegrain-oriented electrical steel sheet according to the item (1), havingε_(OC) and ε_(OL) satisfying the following expressions;1.0×10⁻⁶≦ε_(OC)<3.0×10⁻⁶ 0.5×10⁻⁶≦ε_(OL)<1.0×10⁻⁶, and having ε_(17C)and ε_(17L) satisfying the following expressions;0.5×10⁻⁶≦ε_(17C)<1.5×10⁻⁶ ε_(17L)<0.3×10⁻⁶.
 6. A method for producing alow iron loss and low noise grain-oriented electrical steel sheetcontaining Si: 1.0-4.0 wt% comprising the step of; applying a totalamount of tension of more than 14 MPa which is obtained by a primaryfilm formed by a finish annealing and a secondary film formed bysubsequent processes, and irradiating laser beam in an amount ofheat-input of 1.5-3 mJ/mm² to the specific unit of area of the steelsheet.